Rocky Road: Louis Dollo

Louis Dollo

Louis Antoine Marie Joseph Dollo completed his degree in civil engineering in 1877. He devoted five years to industrial pursuits, then left his homeland of France for Belgium. Working at the Musée Royal d'Histoire Naturelle de Belgique, he concentrated primarily on Iguanodon, the dinosaur originally discovered and named by Gideon Mantell.

From The Dinosaur Papers edited by Weishampel and White

Dollo's timing was fortunate. In 1878, an underground coal mine in southeast Belgium proved to be the final resting place of 31 well-preserved Iguanodon dinosaurs. Dollo oversaw the preparation and articulation of the skeletons, and in 1882, published the first of several papers about the fossils. He discussed the preservation of the skeletons, identified two separate species and addressed their posture. Dollo advocated a bipedal, kangaroo-like stance for Iguanodon. The posture has since been overturned, but paleontologists do acknowledge that Iguanodon probably stood primarily on its hind legs. Dollo speculated that Iguanodon was amphibious and used its powerful tail to swim like crocodiles. He also found that the "horn" that Mantell originally placed on the animal's snout was really a thumb spike.

Dollo's background as an engineer was evident in his writing style, which was concise, direct and usually in numbered paragraphs or lists. When addressing two different forms of Iguanodon, he reasoned as follows.

Either the small form is a young animal and the large one represents the adult state;
Or we are in the presence of variations of either sexual or individual nature;
Or we are dealing either with two species, or with two distinct genera.

Besides his extensive studies of Iguanodon, Dollo helped establish what is now known as paleobiology. He found that detailed studies of fossil anatomy could be used to reconstruct the adaptations of extinct animals. In 1893, he established Dollo's Law, also known as the Law of Irreversible Evolution. He hypothesized that organisms could evolve particular specializations but could not later lose those specializations. Horses, for example, could not re-evolve the side toes they had already lost.

For more information:
The Dinosaur Papers edited by Weishampel and White
The Reign of the Dinosaurs by Jean-Guy Michard